Sea-level rise, localized subsidence, and increased storminess promote saltmarsh transgression across low-gradient upland areas

Miller, Carson B.; Rodriguez, Antonio B.; Bost, Molly C.

doi:10.1016/j.quascirev.2021.107000

Cited by 18 publications

(7 citation statements)

References 101 publications

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“…Several previously established relationships between macro-scale environmental variables and forest mortality were found to be insignificant drivers of threshold elevation in our analysis. For example, storms act as a pulse disturbance that potentially results in rapid forest retreat (Fagherazzi et al, 2019;Miller et al, 2021;Ury et al, 2021). Hurricane Isabel, the largest named storm to affect the region since 1954, had storm surge reaching 2.4 m above highest astronomical tide in some areas of Chesapeake Bay and inundation which lasted for several days (Beven & Cobb, 2004).…”

Section: Tablementioning

confidence: 99%

Biophysical Drivers of Coastal Treeline Elevation

Molino,

Carr,

Ganju

et al. 2023

JGR Biogeosciences

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Sea level rise is leading to the rapid migration of marshes into coastal forests and other terrestrial ecosystems. Although complex biophysical interactions likely govern these ecosystem transitions, projections of sea level driven land conversion commonly rely on a simplified “threshold elevation” that represents the elevation of the marsh‐upland boundary based on tidal datums alone. To determine the influence of biophysical drivers on threshold elevations, and their implication for land conversion, we examined almost 100,000 high‐resolution marsh‐forest boundary elevation points, determined independently from tidal datums, alongside hydrologic, ecologic, and geomorphic data in the Chesapeake Bay, the largest estuary in the U.S. located along the mid‐Atlantic coast. We find five‐fold variations in threshold elevation across the entire estuary, driven not only by tidal range, but also salinity and slope. However, more than half of the variability is unexplained by these variables, which we attribute largely to uncaptured local factors including groundwater discharge, microtopography, and anthropogenic impacts. In the Chesapeake Bay, observed threshold elevations deviate from predicted elevations used to determine sea level driven land conversion by as much as the amount of projected regional sea level rise by 2050. These results suggest that local drivers strongly mediate coastal ecosystem transitions, and that predictions based on elevation and tidal datums alone may misrepresent future land conversion.

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Section: Tablementioning

confidence: 99%

Biophysical Drivers of Coastal Treeline Elevation

Molino,

Carr,

Ganju

et al. 2023

JGR Biogeosciences

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“…However, it is unclear to what extent the predicted magnitude of forest loss will be realized, as multiple lines of evidence suggest that coastal forest retreat may not be synchronized with rising seas (Chen & Kirwan, 2022b; Schieder & Kirwan, 2019) and that other factors also play a role in modulating fine‐scale patterns of coastal tree line dynamics (Fagherazzi et al., 2019; Poulter et al., 2009). For example, site‐specific stratigraphic reconstructions over the past 2000 years suggest periods of time where upland conversion was slower (Schieder & Kirwan, 2019) or faster (Miller et al., 2021) than concurrent RSLRR. These reconstructions are consistent with field observations of mature trees that persist for decades under chronic flooding and salt stress (Field et al., 2016; Kirwan & Gedan, 2019; Poulter, Christensen, et al., 2008; Williams et al., 1999), and the paradigm that storms are necessary to facilitate forest retreat (Fagherazzi et al., 2019).…”

Section: Introductionmentioning

confidence: 99%

Upland forest retreat lags behind sea‐level rise in the mid‐Atlantic coast

Chen,

Kirwan

2023

Global Change Biology

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Ghost forests consisting of dead trees adjacent to marshes are striking indicators of climate change, and marsh migration into retreating coastal forests is a primary mechanism for marsh survival in the face of global sea‐level rise. Models of coastal transgression typically assume inundation of a static topography and instantaneous conversion of forest to marsh with rising seas. In contrast, here we use four decades of satellite observations to show that many low‐elevation forests along the US mid‐Atlantic coast have survived despite undergoing relative sea‐level rise rates (RSLRR) that are among the fastest on Earth. Lateral forest retreat rates were strongly mediated by topography and seawater salinity, but not directly explained by spatial variability in RSLRR, climate, or disturbance. The elevation of coastal tree lines shifted upslope at rates correlated with, but far less than, contemporary RSLRR. Together, these findings suggest a multi‐decadal lag between RSLRR and land conversion that implies coastal ecosystem resistance. Predictions based on instantaneous conversion of uplands to wetlands may therefore overestimate future land conversion in ways that challenge the timing of greenhouse gas fluxes and marsh creation, but also imply that the full effects of historical sea‐level rise have yet to be realized.

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“…We note that there are indeed still limitations to our numerical modeling framework in characterizing the local dynamics needed to accurately predict regional marsh resilience. First, this model is aspatial, that is, the Cohort Marsh Equilibrium Model does not account for horizontal transgression, which has been shown to be a critical mechanisms for predicting how marshes will expand or contract in area in response to sea level rise ( Holmquist et al., 2021; Miller et al., 2021). Second, the Cohort Marsh Equilibrium Model lacks some nuance in vegetation parameters.…”

Section: Discussionmentioning

confidence: 99%

Cohort Marsh Equilibrium Model (CMEM): History, Mathematics, and Implementation

Vahsen,

Todd‐Brown,

Hicks

et al. 2024

JGR Biogeosciences

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Marsh accretion models predict the resiliency of coastal wetlands and their ability to store carbon in the face of accelerating sea level rise. Most existing marsh accretion models are derived from two parent models: the Marsh Equilibrium Model, which formalizes the biophysical relationships between sea level rise, dominant macrophyte growth, and elevation change; and the Cohort Theory Model, which formalizes how carbon mass pools belowground contribute to soil volume expansion over time. While there are several existing marsh accretion models, the application of these models by a broader base of researchers and practitioners is hindered because of (a) limited descriptions of how empirically derived ecological mechanism informed the development of these models, (b) limitations in the ability to apply models to geographies with variable tidal regimes, and (c) a lack of open‐source code to apply models. Here, we provide for the first time an explicit description of a mathematical version of the Cohort Theory Model and a numerical version of a combined model: the Cohort Marsh Equilibrium Model (CMEM) with an accompanying open‐source R package, rCMEM. We show that, through this “depth‐aware” model, we can capture how tidal variation impacts broad patterns of marsh accretion and carbon sequestration across the United States. The application of this model will likely be imperative in predicting the fate and state of coastal wetlands and the ecosystem services they provide in an era of rapid environmental change.

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Sea-level rise, localized subsidence, and increased storminess promote saltmarsh transgression across low-gradient upland areas

Cited by 18 publications

References 101 publications

Biophysical Drivers of Coastal Treeline Elevation

Biophysical Drivers of Coastal Treeline Elevation

Upland forest retreat lags behind sea‐level rise in the mid‐Atlantic coast

Cohort Marsh Equilibrium Model (CMEM): History, Mathematics, and Implementation

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